Great, I checked out the Advantek web-site. It looks good. I do plan to put in a bathrrom in the basement and wanted to tile over the insulated floor. Somone else said I should use Ditra board over the foam board insulation. Should I put the Advantek down first and then the Ditra board over that?

I would probably subfloor the entire basement. If the subfloor is sound and you don't need waterproofing, then you don't need Ditra...you would use a backer of your choice. Thin set it down and screw it to the subfloor.

Installing plywood over the entire floor will also eliminate any floor height differences. 1/4" backer with a 5/16" thick tile should flush out really well.

If you are using floor grade Styrofoam, you should go for a fully floating floor. If you use metal screws, each screw provides a heat bridge to pass your heat to the concrete slab, nullifying the point of insulating.
A fully floating tongued and grooved waterproof plywood floor is best.
Is your floor always dry? What about the walls? Are they dry?